test method
insulation resistance
The insulation resistance test can run on both Class I and Class II devices. It checks whether the ohmic insulation resistance a limit value specified in the standards. The test is performed to determine whether device under test leakage currents can occur in device under test .
If the insulation resistance is insulation resistance low (and there may be a protective conductor fault), the contact voltage on metal parts of the device may be too high. If these metal parts are touched, the so-called touch current would then flow to earth via the person.
On Class II devices, an insulation fault can be dangerous for metal parts, as it is protective earth conductor possible to divert the current via the protective earth conductor .
The insulation resistance is measured by applying a 500-volt DC TEST VOLTAGE the live conductors against earth. The live conductors are often connected to each other. In this case, the total resistance of all insulation resistors connected in parallel is determined during the test.
Since the test is performed with DC voltage, the insulation capacities have no influence on the test. Only the ohmic insulation resistances are determined.
If the insulation capacities are large, the insulation resistance test must take a little longer so that the insulation capacities can charge up at the start of the test. This may take a few tenths of a second, as the Test current is limited Test current a maximum of 3 mA during the insulation resistance test.
Insulation resistance tests are often performed at multiple test points by manually scanning the test points using safety test guns.
However, fully automatic test devices with an extensive matrix (switching fields) can also be set up for automatic testing at several HV test points. There is virtually no limit to the number of matrix points.
Easy switch-over to Test from different test points against a central test point, e.g., the PE.
Two-wire matrix for Test between any test points according to the "everyone against everyone" method.
The insulation resistance test is performed under complex theoretical consideration on an equivalent circuit diagram consisting of four basic components.
These are:
- C = Capacitor between the two poles
- Rs= Surface resistance
- Rpi+Cpi= equivalent circuit diagram of the polarization index
- Riso= insulation resistance
Why?
The device under test an insulation resistance the two test points. This is the resistance Riso. This resistance is usually very high, ranging from several 100 MΩ to 10 TΩ.
Furthermore, the device under test has device under test Capacitance the two test points. This is formed either between the windings to be tested or from the winding to the body. Between the windings, it is usually smaller than from the winding to the body. Capacitances arise between insulated metal surfaces. The larger the surfaces or the smaller the distance between the metal surfaces, the greater the Capacitance. In stator , the windings stator one metal surface and the laminated core forms laminated core other. The larger the stator the size), the larger the surfaces and thus the Capacitance.
Häufig hat ein Elektroprodukt blanke unisolierte elektrische Leiter. Dies gilt z.B. für einen Gleichstrommotor. Auf der Oberfläche der Leiter können sich elektrisch leitende Stäube ablagern und/oder Luftfeuchtigkeit niederschlagen. Dadurch ergibt sich eine Art Oberflächenwiderstand. Im Idealfall sollte er unendlich sein, aber manchmal kann er extrem niedrig werden (< 1 MΩ).
Electrical insulating materials such as resins have dipole-like molecules. These therefore exhibit +/- polarization. When a high-voltage DC is applied, these molecules align themselves with the electric field. The polarization requires a certain amount of time. This is to be simulated using the RC circuit.
What currents result from this?
Theinsulation resistance isinsulation resistance using Ohm's law. After applying the TEST VOLTAGE , a total current (Iges) TEST VOLTAGE , which consists of 4 individual currents.
Total current =Iges=Ic+Is+Ipi+Iiso
This is:Rgiso=Uhv/Iges
The two streams Ic and Ipi only returns to zero after a certain amount of time, this time must be waited for in order to accurately determine the insulation resistance.
The capacitor charges quickly and is usually completed after a few seconds. The goal is to charge the capacitor within a maximum of 30 seconds. After this time, Ic is 0.
Charging the polarization capacity takes considerably longer. In the worst case, this can take electric motor 10 minutes on an electric motor . Under such conditions, the true insulation resistance can therefore only be insulation resistance after 10 minutes.
What testing equipment does SCHLEICH supply SCHLEICH
- Individual test devices
- Combination testers (combination with other safety or functional tests)
- Various versions up to the range of 10 TΩ
- Manual testing using test probes
- Fully automated tests
- Matrix with up to 500 terminals and fully automatic switch-over
- Testing equipment for various device classes
standards bodies
For legal reasons, we are often unable to make any binding statements regarding test conditions. The currently valid standards for the product to be tested are decisive for its application.
The standard may vary depending on the geographical location where the product is used. Further information can also be found at the institutes listed below.
